Products from an imidazole and sulfur dioxide, compositions containing them, and methods of preparation

ABSTRACT

The disclosed compounds are adducts of imidazole or derivatives thereof and sulfur dioxide. The adducts are apparently of the Lewis acid-Lewis base type, and are useful as latent curing agents for epoxide resins. The adducts are prepared by interacting the imidazole and sulfur dioxide under anhydrous conditions. Equimolar imidazole-SO2 adducts can serve as a source of sulfur dioxide at room temperature.

United States Patent [191 Sweeny et al.

[451 Oct. 1,1974

[ PRODUCTS FROM AN IMIDAZOLE AND SULFUR DIOXIDE, COMPOSITIONS CONTAININGTHEM, AND METHODS OF PREPARATION [75] Inventors: Norman P. Sweeny, NorthOaks,

Minn.; Karl Friedrich Thom, Cologne, Germany [73] Assignee: MinnesotaMining and Manufacturing Company, St. Paul, Minn.

22 Filed: June 14, 1972 21 Appl. No.: 262,557

[52] U.S. Cl. 260/47 EN, 260/2 N, 260/18 PF, 260/37 EP, 260/45.8 N,260/59, 260/78.4

EP, 260/94.7 S, 260/309 [51] Int. Cl C08g 30/14 [58] Field of Search260/47 EN, 2 N, 309, 59, 260/2, 18, 94.7, 78.4 EP

[5 6] References Cited UNITED STATES PATENTS 3,356,645 l2/l967 Warren260/47 OTHER PUBLICATIONS Chem. Abst., Vol. 71, Synthetic High Polymers,1969 (p. 7l0l2g).

Chem. Abst., Vol. 72, Nonferrous Metals'and Alloys, 1970 (p. 1245870).

Primary ExaminerWilliam H. Short Assistant ExaminerT. Pertilla Attorney,Agent. or Firm-Alexander, Sell, Steldt & DeLaHunt [5 7] ABSTRACT 5Claims, N0 Drawings PRODUCTS FROM AN IMIDAZOLE AND SULFUR DIOXIDE,COMPOSITIONS CONTAINING THEM, AND METHODS OF PREPARATION FIELD OF THEINVENTION DESCRIPTION OF THE PRIOR ART It is well known that sulfurdioxide is a Lewis acid, though not nearly so strong a Lewis acid as,for example, boron trifluoride. It is also known that nitrogen bases(e.g. amines) are Lewis bases and can react with sulfur dioxide to formadducts. The literature relating to such adducts is extensive,representative examples being W. C. Fernelius, Ed., Inorganic SynthesisII,

McGraw-Hill, NY. (1946); W. E. Byrd, Inorganic Chemistry 1, p. 762(1962); K. R. Hoffman ,et al, J. Am. Chem. Soc. 68, p. 997 (1946), H. A.Hoffman et "al, J. Am. Chem. Soc. 70, p. 262 (I948). The Byrd articleindicates that the exact structure of aromatic amine-sulfur dioxidecomplexes is not well understood, since it is possible that the sulfurdioxide could be bound to the adduct via the pi-complex of the aromaticring. The picture is further complicated by data in the Byrd article andboth Hoffman et al articles indicating that some of these aromatic (orheterocyclic-aromatic) amine-sulfur dioxide adducts or complexes areunstable, though there is little doubt that true adducts, rather thansimple mixtures, are formed.

According to U.S. Pat. No. 2,270,490 (Wood), issued January, 1942,morpholine and sulfur dioxide react to form a compound useful as aphotographic developer, local anesthetic, or antioxidant, but in thiscase it is suggested that the compound can be a true salt, i.e. a saltof the cation-anion type. Some of the aromatic amine-sulfur dioxideadducts exhibit crystalline character and have sharp melting points, butprobably lack this high degree of ionic character. The nature of theamine (aliphatic, aromatic, aromatic heterocyclic, non-aromaticheterocyclic, etc.) appears to have significant effects upon the natureof the sulfur dioxide adduct or compound, but these effects have notbeen explored fully enough to postulate any general rules for all thepossible adducts.

Apparently none of these prior art adducts or compounds has beeninvestigated for use as a latent catalyst or initiator or curative inepoxy resin technology, though amines per se have been investigatedextensively. Several different Lewis acid-Lewis base adducts of theamine-boron trifluoride type have been carefully studied by epoxy resinchemists. and various theories have been proposed to explain theirpotency or latency, as the case may be, in curing diglycidylether-bisphenol A epoxides at various cure temperatures. See, forexample, Harris et al, J. Appl. Polymer Science 10, p. 523 (1966). TheHarris et al article provides little or no guidance for one attemptingto use a Lewis acid-Lewis base adduct derived from sulfur dioxideinstead of boron trifluoride. The degree of latency of an amine BFadduct appears to be independent of its stability (Harris et al, opcit., pp. 523525 and 527), but the stability of amine S0 adducts is sovariable that latency might very well be a function of the stability ofthe adduct.

imidazole and its derivatives have been used as nonlatent initiators orcurative-catalysts for epoxide resins, and various approaches have beenused .to make latent compounds or complexes containing imidazole nuclei;see, for example, U.S. Pat. No. 3,553,166 (Anderson et al.), issued Jan.5, l971. Apparently, imidazole-sulfur dioxide adducts have never beenreported in the literature and have never been proposed for use as epoxycuring agents or for any other purpose. In view of the variations in thestability of different types of aminesulfur dioxide adducts and the lackof guidance in the prior art as to their behavior as epoxy initiators,it would be difficult at best to predict the stability and utility of animidazole-sulfur dioxide-adduct. Nor is it even possible to predict withcertainty from the available prior art if such an adduct can even bemade and what its structure might be. Analogies between imidazole andother heterocyclic and/or aromatic and/or aliphatic amines are difficultto draw, due to the uniqueness of the imidazole nucleus I Accordingly,this invention contemplates synthesizing adducts from imidazole orderivatives thereof and ing either curable latentepoxy resin systems orstabilized acrylate monomers containing the adducts.

SUMMARY OF THE INVENTION Briefly summarized, the present inventioninvolves the synthesis of imidazole-sulfur dioxide adducts and thediscovery that these adducts are useful both as a source for an acidicstabilizer and in the formulation of latent curable epoxides. Theselatent curable systems have a shelf life of weeks or months (e.g. atleast 6 months) and are rendered non-latent at elevated temperatures(e.g. above 50 C., preferably above C.); that is, the typical epoxidecuring reactions can be made to occur expeditiously at these elevatedtemperatures. The compounds of this invention can be prepared byexposing imidazole or a derivative thereof (optionally dissolved in asolvent) to liquid or gaseous sulfur dioxide, or a saturated solutionthereof, under anhydrous conditions for a period of several minutesuntil the compound precipitates out as a solid sulfur dioxide-imidazoleadduct. The apparent behavior of these solid products in the presence ofcurable epoxy resins is evidence not only of utility, but also of astable, adduct-like structure, as opposed to a mere physical mixture.The adducts decompose upon heating into sulfur dioxide and imidazole (oran imidazole derivative) and thereby serve as a latent source for eitherthe imidazole or sulfur dioxide.

DETAILED DESCRIPTION Adduct-like compounds made according to the presentinvention can be represented by the following formula:

(lmid),,.SO-;

wherein lmid is imidazole or a derivative thereof, Le. a nucleus of theformula stituents or hydrogen, the preferred substituents beingnon-hindering organic radicals such as alkyl or aryl radicals or,particularly in the case of R and R, fused rings. For convenience, theterm an imidazole or an imidazole nucleus is used in this specificationto denote both imidazole itself (C N l-l and the imidazole derivativesof formula (lI),'set forth previously.

The term curing agent is used to denote agents which assist orparticipate in hardening or crosslinking or polymerization reactionswhich solidify or increase the viscosity of liquid epoxide monomers orprepolymers or convert solid epoxides to tough, durable thermosetmaterials. Curingagents" are referred to as hardeners" orffcrosslinkersin some contexts, be-

Adducts of an imidazole and sulfur dioxide can be synthesized by one ofthe following methods, provided that anhydrous conditions aremaintained.

1. An imidazole is dissolved in a solvent such as acetonitrile andgasoues sulfur dioxide 'is bubbled through thesolution. An exothermicreaction occurs. Upon dilution with the solvent, a white precipitateforms which is the imidazolesulfur dioxide adduct. 7

2. Gaseous sulfur dioxide can be passed over an imidazole and the adductforms. The solid adduct may be recovered fromthe reaction mass bytreating it with a solvent.

3. A solution of an imidazole in a solvent can be added to anotherportion of a similar or the same solvent which is saturated with sulfurdioxide. A precipitate is formed which is the imidazole-sulfur dioxideadduct.

4. Liquid sulfur dioxide can be added to an imidazole (either as thepure compound or as a solution of the compound) and theadduct forms. Themixture is treated with a solvent to recoverthe solid adduct.

gases to act as carriers and controls for'the exothermic reaction.

The 2:1 adducts (2 imidazolezl S0 are more stable than the 'l'zladducts. Sulfur dioxide loss occurs with cause of their abilityto-convert even the liquid monomers or prepolymers to thermoset solids.It is also common in the art to refer to imidazole as a catalyst orinitiator" since it assists in the opening of the oxirane ring. However,it is established that imidazole can make a contributionto theproperties of the cured epoxideandis thus more than a simple catalyst.For consistency tures, and the storable system can be said tohave goodstorage stability or a long shelf life or pot-life. The shelf life'of aliquid one-part system can be convenientlydetermined by observing itsviscosity; any tendency toward premature gelation'will, ofcours'e, be'evidenced by an increase inviscosity.

1:1 adducts at room temperature over a period of three to four days. Theequation for this decomposition is:

wherein lmid is as defined previously.

It is difficult to removethe'last traces of solvent from. the compounds;of Formula (I), and mixture of comone value, eg 2 and i v I 7 heat V mif" (Imid)n -S 02 n Imid S 0M1) (I) (In (Eq.

For a, given lmid moiety, the dissociation temperatures of the compoundsof. formula (I) can vary when W varies. For example, for.,l,Z-dimethylim-idazole, the dissociation temperature -of the .n f 2species is higher than that of the n 1 species ..The properties of Acured epoxide systems which have been obtained by heating the curablelatent systems containingformula (1) compounds can also vary with n fora given lrnid moiety. The dissociation temperatures are not fixedprecisely, but generally appear to be significantly higher than roomtemperature. Undernormal ambient temperature and pressure, 'e.g. 23(1/760 mm of Hg,

dissociation of the 1:1 (i.e."n 1), 2:1 nq= and 3il (ri 3) adductsaccording to' Equation 2 is, to say the least, difficult'todetect.Experimentationlwith curable epoxide materials such as diglycidyl ethersof bisphenol A shows that the adducts have little, if any, effect uponthe viscosity of the epoxide over a period of months, indicating anepoxide pot life longer than 6 months. This pot life data indicates thatlittle or no free imidazole or imidazole derivative is available forinteraction with the vicinal epoxide (oxirane) ring, since freeimidazole can cure typical curable epoxide systems in a manner ofminutes at room temperature; see Farkas et al, J. Appl. Polym. Sci. 12,159 (1968). Even the latentizing of imidazole with acetic acid to formimidazole acetate salts extends the pot life of the epoxide system toonly about three weeks; see US. Pat. No. 3,356,645 (Warren), issued Dec.5, 1967. Thus, a simple comparison with known curable epoxide systemsprovides further evidence that the adducts of the present invention arereasonably stable compounds at normal ambient temperature and pressure,at least insofar as loss of the imidazole moiety is concerned. Someclearly detectible loss of imidazole can occur at temperatures above themelting points of the adducts, particularly in the range of 100 200 C.,as is subsequently shown by the data Table I]. Since the adducts havevarying degrees of stability at temperatures above 100 C.. the rate orextent of dissociation can be selected in accordance with the desiredrate of cure or gel time, as the case may be. To illustrate: given atemperature of 180 C. and a typical latent curable system containing aformula (I) compound of this invention, the gel time is much longer forlmid benzimidazole than for Imid imidazole (C N H At 160 C., thebenzimidazole adduct appears to have little or no effect upon adiglycidyl etherbisphenol A epoxide prepolymer; but the imidazoleadducts are very effective at this temperature. The l-alkyl imidazolespecies of Formula (I) also exhibit longer gel times. The properties ofthe cured epoxides obtained according to this invention are generallysatisfactory.

The compounds of Formula (I) are generally solids with fairly smallmelting ranges, typically not more than 5 Centigrade degrees. These datacan be compared to the 80-85 C. melting range of morpholine-sulfurdioxide, which is reported to be a salt-like chemical compound in theUS. Pat. No. 2,270,490 referred to previously. The compound (lmid);;.SOwhere Imid 2- ethyl-4-methylimidazole, appears to be a viscous liquid,but, as shown subsequently by Table I, this is not typical.

Formulation of curable epoxide systems containing curing agents of thisinvention can be carried out along the lines generally laid down bylatent imidazole epoxide curing technology, e.g. the technologydescribed in the aforementioned US. Pat. Nos. 3,553,166 and 3,356,645.The US. Pat. No. 3,553,166 also describes suitable co-curatives (e.g. ofthe dicyandiamide type) which can be included in the curable system. itis preferred to introduce at least 0.1 percent by weight, based on theweight of the epoxide monomer or prepolymer, of a compound of Formula(1) into the curable system, and levels of l-2O percent by weight areparticularly useful. Levels higher than percent even 50 percent or moreare permissible but excessively increase the cost of the system withoutany significant beneficial result.

Typical one-part curable epoxy resin systems formulated according tothis invention comprise (l) 0.1 20 parts by weight of a curing agent ofFormula (I), (2) at least 80 parts by weight of a suitablecycloaliphatic, aliphatic, aromatic, or heterocyclic epoxide, and (3) 0300 parts by weight of suitable fillers, extenders, flexibilizers,pigments, and the like, e.g. colloidal silica. These one-part systemshave sufficient shelf-life at normal ambient temperature to allow formost ordinary shipping and inventory procedures, although the stabilityof the system can be further enhanced, if desired, by specialprecautions such as careful temperature control during storage. It isgenerally not necessary to formulate two-part systems (with the epoxidein one container and the curing agent in another). If a two-part systemis made up, however, the benefits of this invention will still beapparent to industrial users who blend the two parts and then carry outone or more coating, molding, laminating, casting, or impregnating stepsprior to curing at cure temperatures above C. These steps can be carriedout in a leisurely fashion, taking advantage of the long roomtemperature pot life prior to curing at elevated temperatures.

Epoxides suitable for use in this invention can be aliphatic,cycloaliphatic, aromatic or heterocyclic and will typically have anaverage epoxy equivalency (i.e. the number of epoxy groups contained inthe average molecule) of from about 1.7 to 6.0, preferably 2 or 3, thisvalue being the average molecular weight of the epoxide divided by theepoxide equivalent weight. The epoxy equivalent weight, which isdetermined by multiplying the same weight by 16 and dividing by thenumber of grams of oxirane oxygen in the sample, is typically greaterthan 100 for commercially useful curable systems. These materials arevariously referred to as epoxide monomers or prepolymers and in anyevent can contain repeating units, e.g. repeating ether units. Typicalof such epoxides are the glycidyl-type epoxy resins, e.g. the diglycidylethers of polyhydric phenols and of novolak resins, such as described inHandbook of Epoxy Resins, by Lee and Neville, McGraw-Hill Book Co., NewYork (1967).

Another useful class of epoxides has a structure of the following type:

where Ep is an epoxide ring, R is hydrogen, or a non-hindering aliphaticgroup (e.g. methyl);

R is an aliphatic or aromatic radical; and

z is a number from 0 to about 5.

In Formula W,

n is a numberfrom l to 6.

Typically, these epoxides are glycidyl ethers of polyhydric phenolsobtained by reacting a polyhydric phenol or aliphatic polyol with anexcess of chlorohydrin, such as epichlorohydrin, e.g. the diglycidylether of Bisphenol-A or of resorcinol, 1,4-butane diol, or the like.Further examples of epoxides of this type which can be used in thepractice of this invention are described in US. Pat. No. 3,018,262(Schroeder), issued Jan. 23, 1962.

The preferred cycloaliphatic epoxide monomers or prepolymers preferablycontain at least one 5- or 6- membered carbocyclic ring (or heterocyclicring with equivalent properties) on which is substituted the epoxidefunctional group. In polycyclic cycloaliphatic epoxides, the two ringsare preferably independent and preferably joined by a bridging radicalcontaining at least one ester or ether linkage. A plurality of theseester or ether linkages can provide flexibilizing properties in thecured system. Further examples of cycloaliphatic epoxide compounds aredescribed in US. Pat. No. 3,117,099 (Proops et al.), issued Jan. 7,1964.

There are a host of commercially available epoxides which can be used inthis invention, including the diglycidyl ether of Bisphenol-A (e.g. Epon828, EpiRez 522-C, Araldite" 7072, Epon 1002 and DER 332), mixtures ofthe diglycidyl ether of Bisphenol A with an alkyl glyeidyl ether (e.g.ERL

2795), vinylcyclohexene dioxide (e.g. ERL-4206),

3,4-epoxycyclohexylmethyl-3, 4-epoxycyclohexane carboxylate (e.g.ERL"-422 1 3,4-epoxy-6- methylcyclohexylmethyl-3,4-epoxy-6-methylcyclohexane carboxylate (e.g. ERL-4201bis(3,4-epoxy-6-methylcyclohexylmethyl)adipate (e.g. ERL"-4289),bis(2,3-epoxycyclopentyl)ether (e.g. ERLA"-0400), aliphatic epoxymodified with polypropylene glycol (e.g. ERLA-4050 and ERLA- 4052),dipentene dioxide (e.g. ERL-4269), epoxidized polybutadiene (e.g. Oxiron2001 silicone epoxy (e.g. Syl-Kem 90), 1,4-butanediol diglycidyl ether(e.g. araldite RD-2 polyglycidyl ether of phenolformaldehyde novolak(e.g. DEN-431 and DEN"-438) resorcinol diglycidyl ether (e.g. CibaERE"-l359), and epoxidized unsaturated esters of carboxylic acids havingmore than six carbon atoms, e.g. epoxidized soybean oil. (Epon" is atrade-mark of Shell Chemical Co.; EpiRez is a trademark of Jones- DabneyCo.; Araldite is a trademark of Ciba Products Co.; the various DER" andDEN designations are trade designations of Dow Chemical Co.; the ERLdesignations are trade designations of Union Carbide Plastics Division;Syl Kem" is a trade designation of Dow Corning; Oxiron is a trademark;and ERE-1359" is a trade designation of Ciba Products Co.)

The compounds of Formula (I) and the nuclei of Formula (II) have alreadybeen described in some detail. As will be apparent from thisdescription, the substituents R R R, and R can be varied considerablywithout any adverse effect upon the operability of this invention. Theteachings of the aforementioned US. Pat. Nos. 3,356,645 and 3,553,166,and of US. Pat. No. 3,361,150 (Green), issued Dec. 28, 1971, aregenerally applicable here with respect to selection of imidazolesubstituents, which can also include 5- and 6-member fused or separateheterocyclic or carbocyclic rings. Substitution at the 1- position (i.e.R a H) is least preferred. Lower alkyl substituents (includingsubstituted lower alkyl) are generally most preferred, although higheralkyl substituents (containing, for example, 7 36 carbons) can be used.Other aliphatic (including substituted aliphatic) radicals can besubstituted, as is conventional. Included among these are the alkenyland alkinyl radicals such as allyl. Fused rings (such as fused benzeneor other 6-member carbocyclic rings) are preferably attached to the 4and 5 positions; thus R and R together can comprise the three or fourcarbons or heterocyclic atoms of a fused ring. Separate aromatic ringscan be substituted at the 1-, 2-, 4-, or 5- (preferably the 2-, 4-, or5-) positions and can be monocyclic (e.g. phenyl, tolyl, xylyl, etc.) orpolycyclic (preferably dior tri-cyclic, e.g. naphthyl).

As pointed out previously, the compounds of Formula (l) are generallyuseful when a latent source or other controlled release of either animidazole or sulfur dioxide is needed.

For example: alpha-cyanoacrylate monomers of the formulaCH-,-=(C(CN)COOR, wherein R can be alkyl, phenyl, alkoxy, etc,polymerize by an ionic mechanism and are sensitive to contaminants, e.g. moisture. A considerable body of patent and scientific literature isavailable concerning the use and storage of these monomers; see US. Pat.No. 2,776,232 (Shearer et al.), issued Jan. 1, 1957, British Patent No.1,159,548 (Rice et a1.) published July 30, 1969, US. Pat. No. 3,483,870(Coover et al.), issued Dec. 16, 1969, and British Patent No. 1,048,906(Halpern et al.), published November 23, 1966. A commercially availableexample of a cyanoacrylate monomer is Eastman 910, trade designation ofEastman Kodak Company. Sulfur dioxide has conventionally been used tostabilize these monomers. It has now been found that a compound ofFormula (1), preferably one wherein n 1, can be used as a source ofconstant sulfur dioxide pressure to preserve these monomers in a closedsystem.

The principle and practice of this invention is illustrated by thefollowing non-limiting Examples, wherein all parts are by weight unlessotherwise specified.

EXAMPLE 1 Ten grams of imidazole were placed in a 250 ml. Erlenmeyerflask and exposed to gaseous sulfur dioxide for fifteen minutes.lmmediate reaction takes place as is indicated by an exotherm. A lightyellow viscous liquid is obtained. An increase in weight of nine gramsresulted. (This liquid will cure epoxy resins immediately and shows nolatency). The viscous liquid is subsequently treated with 150 ml. CHCL,and stirred rapidly. A fine white precipitate is formed and slowevaporation of the solvent yields 18.5 gms. of product. Drying at roomtemperature under vacuum for three hours yields 16.5 gms. of material.(m.p. 100- 104; 19.9% N; 19.8% S; [N]/[S] 2.30.)

The one:one adduct of imidazole and sulfur dioxide is a latent curingagent for epoxy resins. Five parts of the adduct admixed with parts ofepoxy resin (Epon 828) shows no increase in viscosity over a period ofmonths. At C., this mixture has a gel time in excess of 30 minutes,whereas a similar mixture of imidazole and epoxy has a gel time of fiveminutes.

The one:one adduct shows a slow decomposition to the twozone adduct.This decomposition is shown by an almost linear decrease in sampleweight over a period of about 75 hours. There was no further change insample weight from the 80th to the th hour, and weighings were thendiscontinued.

EXAMPLE 2 Two moles (136 gm) of imidazole were placed in a three-neckflask fitted with a condensor, a gas inlet tube, and a stirrer. Theimidazole was dissolved in 200 cc. of chloroform. Gaseous sulfur dioxide(one mole) was bubbled into the solution through the inlet tube as thesolution was stirred. After the addition of the sulfur dioxide, stirringwas continued for one hour. The solution was transferred to a Rotovaporand the solvent evaporated off at room temperature. A white solid wasobtained upon removal of the solvent. (M.p. 70 C; 21.0% N; 12.9% S;[N]/[S] 3.71.) The elemental analysis indicated that the compound islmid2SO2,

imidazole (Example 3); 2-methyl imidazole (Example 4); l,2-dimethylimidazole (Example 5); Z-ethyl, 4- methyl imidazole (Example 6); andbenzimidazolc (Example 7). Data on these compounds or adducts is setwhere lmid imidazole. The solid showed no weight 5 forth in Table I. Themelting point of morpholine-sulfur loss over a period of months. dioxideis also given in Table I'for comparison.

Five parts of the solid were added to 100 parts of Examples 8 H aretabulated m Table H and 828 (Trademark of She Chemical Company) tratethe use of the compounds of Examples 1 2, 5, and resin, which is adiglycidyl ether of Bisphenol A. A porlo 7 with if epcgxldea l epmilde fq' tion of this mixture was immediately heated to l60 C. Tg ifg l i f TThe sample cured toahard resin in less than three mini y" 0 e emlcautes. The Barcol hardness of the resulting cured sample vlscqub hqulfjdlglycldyl ethef of blsphenol A havmg was 85. Another portion of themixture was stored on epmflde equivalent weight Shghflx gleam the thelaboratory shelf for 3 months during which time no oretical 170 and anepoxide functionality of slightly less than 2.0). In Examples 8. 9, lOA,and 11A, 95 percent change m the conslstency of the res1n was noted. Theb h f h d 3-month-old portion was warmed to 160 c.. and 1;" to t g ag gcured at this temperature to a hard resin in less than iffy g gg 2; 22352: 3 335 51 three minutes. The Barcol hardness of this cured resin 6 aercent of g e i is comlined with 10 wt was 85. (A resin system isconsidered cured when it erceltpof the Com g of Exam es 5 and 7 res lhas reached the most advanced state of hardening for I F I d that Systemtlve y. or comparison, ataon wt. percent iml azole, benzimidazole, andl.2-d1methyl imidazole are also shown in Table II; the epoxide is againEpon 828. EXAMPLES 3 TO 11 In Table ll. the Barcol Hardness test is thestandard In Examples 3 to 7, imidazole-sulfur dioxide adducts 935 ASTMtest. Gel time is a measure of the length were prepared in the samemanner as Example 2 from oftime a sample of resin may be maintained in apliable sulfur dioxide and the following imidazoles: l-methyl form at agiven temperature.

' TABLE I Adducts of imidazoles and sulfur dioxide Found Calculated,Percent percent Ex. Adduct M.P. N s [NJ/[S] N v s N NH-SO2 [N N-HJ-SO:

[N N-oHiI-SO; 2

N N-H N N-CHa-SO,

N N-H -SO2 N O -SO2 a /i s0,s5

0 /NH- S 02 1 Viscous liquid.

*Patent N 0. 2,270,490.

TABLE II Examples 8 ll M GEL TIME minutes:seconds At: I Barcol HardnessEx. Compound of (wt. 7r) 100C. 120C, 140C, 160C. 180C. 200C. of CuredProduct 8 Example 1 30 min: 9 min: 2 min: 1 min: I

21 sec. 19 sec. 21 sec. 41 sec. 84

9 Example 2 5 41 min: 21 min: 4 min: 2 min: 1 min:

5 sec. 27 sec. 40 sec. sec. 44 sec. 84

10A Example 5 5 90 min. 93 min: 85 min. 2 a 35 sec. 85

108 Example 5 10 I 17 min: 2 min:

4 sec. 13 sec. 85

11A Example 7 5 90 min. 90 min. 90 min. 80

113 Example 7 1O 11 min: 4 min:

30 sec. 1 1 sec. 80

imidazole 5 5 min: 2 min: 1 min.

3 sec. 40 sec. 24 sec. 15 sec.

benzimidazole 5 55 min: 2 min: 1 min:

18 sec. 40 sec. 1 I sec. 47 sec.

1.2-dimethyl imidazole 5 49 sec. 41 sec. 27 sec. 18 sec.

What is claimed is: l. A latent, curable composition comprising a. aneffective amount of a curing agent of the formula wherein (lmid),..SO

n is a number from 1 to 4, and

lmid is a compound of the formula wherein R, R R and R independentlyrepresent substituents selected from the group consisting of hydrogen,aliphatic radicals and aromatic radicals, and together R and R can bethe residue of a fused ring, and

b. a curable a-epoxide resin having an average epoxy equivalency of 1.7to 6.0.

wherein Ep is an a-epoxide ring,

R is a divalent group selected from the group consisting of aliphaticand aromatic radicals, and

z is a number from about zero to about 5.

5. A latent, curable composition comprising a. an effective amount of acuring agent of the formula (lmid),,.SO

wherein lmid is imidazole, and n is a number from 1 to 4, and b.diglycidyl ether of Bisphenol-A.

1. A LATENT, CURABLE COMPOSITION COMPRISING A. AN EFFECTIVE AMOUNT OF ACURING AGENT OF THE FORMULA
 2. A composition according to claim 1wherein n of said formula is a number selected from the group consistingof 2 or 3 or mixtures thereof.
 3. A composition according to claim 1wherein said composition comprises 0.1 - 20 percent by weight of saidcuring agent.
 4. A composition according to claim 1 wherein said Alpha-epoxide resin is a compound of the formula Ep - CH2(O-R1-O-CH2-CHOH-CH2)z O - R1 - O - CH2 - Ep wherein Ep is an Alpha-epoxide ring, R1 is a divalent group selected from the group consistingof aliphatic and aromatic radicals, and z is a number from about zero toabout
 5. 5. A latent, curable composition comprising a. an effectiveamount of a curing agent of the formula (Imid)n.SO2 wherein Imid isimidazole, and n is a number from 1 to 4, and b. diglycidyl ether ofBisphenol-A.